The present invention relates to net wrapping devices for large round balers and more specifically relates to an arrangement for feeding net from a supply roll of wrap material to the baling chamber of the baler.
Wrapping materials such as plastic sheet or mesh need to be kept under a certain amount of tension while being wrapped about a bale in order for the bale to be tightly wrapped for shedding moisture so as to prevent spoilage of the baled crop material. At the same time, the tension should not be so high as to cause the net to rupture or to be easily torn while being applied to the bale or during handling of the wrapped bale. Current designs of net wrapping devices involve supporting the supply roll of net material on support pads which rub against the exterior of the supply roll as the latter rotates in place as material is pulled off the roll during wrapping of a bale. Temperature and humidity also may affect the frictional characteristics of the plastic wrapping material. While it is known to construct the pads with special surface shapes to lessen the area of contact between the roll of wrap material and the pads and to make the supporting surfaces of these pads of materials, such as stainless steel, so as to provide a smooth, rust free surface, the rotation of the wrap material on the pads generates static electricity which produces "static cling" in the material which may interfere with proper feeding. Further, in order to accommodate for the change in the frictional resistance due to the loss in weight of the supply roll as material is used in wrapping a bale, braking bar arrangements have been designed which include a bar that engages the roll across its width and applies an increasing downward force on the material roll as the material is used. However, the frictional resistance to the rotation of the roll offered by the brake bars themselves is subject to frictional variations caused by temperature and humidity and/or due to variations in the oiliness of the wrap material and/or due to changes in the surface condition of the brake bar. By necessity, extreme smoothness, shape and positional relationship of the pads and the design of the braking bar have to be closely controlled in order to achieve the desired tension control.
U.S. Pat. No. 5,181,368, granted to Anstey et al. on Jan. 26, 1993 discloses a net wrapping device embodying specially shaped, stainless steel covered pads and a braking device, as described above, in an attempt to control the tension in the net wrapping material as it is wrapped about a bale.